U.S. patent number 4,429,236 [Application Number 06/288,406] was granted by the patent office on 1984-01-31 for apparatus for generating pulses upon decreases in supply voltage.
This patent grant is currently assigned to Robert Bosch GmbH. Invention is credited to Werner Nitschke.
United States Patent |
4,429,236 |
Nitschke |
January 31, 1984 |
Apparatus for generating pulses upon decreases in supply
voltage
Abstract
A pulse for resetting computing equipment is generated upon a
drop in the supply voltage. In a first embodiment of a circuit
furnishing such a reset pulse, a comparator is used whose inverting
input is connected to the supply line through a capacitor and to
ground potential through a parallel diode-resistor combination. The
direct input is connected to the tap of a voltage divider and is
connected through a feedback resistor to the output. This circuit
can detect drops in supply voltage in the order of the forward drop
across the diode. Alternatively, a RC oscillator can be used to
generate a reset pulse. If the capacitor in the circuit is not
recharged in time by a pulse furnished by the computing equipment
being controlled, it is assumed that failure to receive the pulse
is indicative of a drop in supply voltage.
Inventors: |
Nitschke; Werner (Ditzingen,
DE) |
Assignee: |
Robert Bosch GmbH (Stuttgart,
DE)
|
Family
ID: |
6112680 |
Appl.
No.: |
06/288,406 |
Filed: |
July 30, 1981 |
Foreign Application Priority Data
|
|
|
|
|
Sep 24, 1980 [DE] |
|
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3035896 |
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Current U.S.
Class: |
327/87; 327/1;
327/31; 327/392; 340/663 |
Current CPC
Class: |
G01R
19/16538 (20130101); G06F 1/24 (20130101); H03K
21/38 (20130101); H03K 5/1536 (20130101); H03K
5/153 (20130101) |
Current International
Class: |
G01R
19/165 (20060101); G06F 1/24 (20060101); H03K
5/1536 (20060101); H03K 5/153 (20060101); H03K
21/00 (20060101); H03K 21/38 (20060101); H03K
005/153 (); G01R 019/165 () |
Field of
Search: |
;307/296R,64,130,362,234,518,2A,608 ;340/661,662,663 ;361/92 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Zazworsky; John
Attorney, Agent or Firm: Frishauf, Holtz, Goodman &
Woodward
Claims
I claim:
1. Apparatus for generating a pulse in response to excessive
changes in the output of an electrical power supply having two
terminals forming a line terminal (1) and a reference terminal,
comprising
a differential amplifier means (6) having a first (+) and second
(-) input and an output from which the pulse is derived;
feedback circuit means (10) connected from said output of the
differential amplifier means (6) to said first input of said
amplifier means;
voltage divider means (7, 8) connected across the terminals of said
power suply and having a voltage divider tap connected to said
first input of said differential amplifier means (6);
a capacitor (2) connected to one terminal of said power supply and
to said second input of said amplifier means;
a resistor (3) connected jointly to said capacitor and also to the
second input of said amplifier means, and further to the other
terminal of said power supply to permit charging of the capacitor
(2) therethrough upon application of supply voltage to said
terminals; and
a diode junction (4) having a forward voltage drop connected in
parallel with said resistor (3),
the voltage divider means (7,8) applying a voltage to said first
input of said differential amplifier means which balances the
voltage applied to said second input of the differential amplifier
means under charged conditions of the capacitor (2),
drop of voltage of the power suply by an amount in excess of the
forward voltage drop across the diode junction permitting discharge
of the capacitor (2) through the diode junction (4) causing
unbalance of the voltages at the first and second inputs of the
differential amplifier means and switch-over of said differential
amplifier means and generation of said pulse.
2. Apparatus as set forth in claim 1, wherein said first input is a
direct input and said second input is an inverting input of an
operational amplifier.
3. Apparatus as set forth in claim 1, wherein said diode junction
comprises a diode (4).
4. Apparatus as set forth in claim 1, in combination with a
microprocessor (M), said output of the differential amplifier means
being connected to a reset terminal (M-R) of the microprocessor,
the microprocessor being connected across the electric power supply
and receiving operating power therefrom.
5. Apparatus for generating a reset pulse in response to excessive
changes in the output of an electrical power supply (11)
comprising
an operational amplifier means (15) having a direct and an
inverting input, and an output from which the pulse is derived;
feedback circuit means (20) connected from said output to said
direct input of said operational amplifier means;
voltage divider means (16, 17) connected to said power supply and
having a voltage divider tap connected to said direct input of said
amplifier means;
a capacitor (12) connected to said inverting input of the
operational amplifier means;
a resistor (13) connected to said capacitor and a first reference
potential;
an additional feedback circuit means (19) connected between said
output of said operational amplifier means and said inverting
input;
controlled switch means (T) interconnected between said resistor
and the first reference potential;
and means (21-25) controlling said switch means to change state at
predetermined intervals in dependence on the voltage of said power
supply, absence of recurring change-of-state of said switch means
causing application of a voltage due to unusual change-of-charge
state on said capacitor, and hence generation of the output
pulse.
6. Apparatus as set forth in claim 5, wherein said power supply is
the supply for a microprocessor;
and said means for controlling the switch means comprises control
circuit means (21-25) connected to said switch means and said
microprocessor for operating said switch means in accordance with
output pulses from said microprocessor.
7. Apparatus as set forth in claim 6, wherein said switch means
comprises a transistor.
8. Apparatus for generating reset pulses to computing equipment in
response to fluctuations in supply voltage, comprising
comparator means (6) having an output for furnishing said reset
pulses, an inverting input, and a direct input;
voltage dividers means connected to said supply voltage, said
voltage dividers means having a tap connected to said direct input
of said comparator means:
feedback means (10) connected from said output to said direct
input; and timing circuit means (2,3,4) having a charging time
constant and a discharge time constant different from said charging
time constant connected to said inverting input so that the voltage
at said inverting input is raised above the voltage at said direct
input in response to increases in said supply voltage and for a
time period depending upon the amplitude of said increases, whereby
a reset pulse having a pulse width exceeding the pulse width of
reset pulses indicative of supply voltage fluctuations is generated
when said voltage is first applied to said apparatus.
9. Apparatus for resetting computing equipment after supply voltage
fluctuations, said computing equipment being adapted to generate
control signals at predetermined time intervals when normal supply
voltage is applied thereto, comprising
a capacitor (12);
means for rapidly discharging said capacitor at a predetermined
rate and resetting said computing equipment when the charge on said
capacitor has reached a predetermined threshold value; and
means (14, 21-25) connected to said capacitor and said computing
equipment for rapidly charging said capacitor in response to each
of said control signals, said capacitor discharging to said
predetermined threshold value only in the absence of said control
signals from said computing equipment.
Description
The present invention relates to electrical circuits for resetting
computing equipment such as microprocessors for defined changes in
supply voltage.
BACKGROUND OF THE INVENTION
In a well-known apparatus, a reset pulse is applied to a
microprocessor when electrical power is first applied. However,
there is no provision made for resetting the microprocessor also
when it may be in some undefined condition due to decreases in the
supply voltage. If the computation is then continued without taking
account of such decreases, large errors in the result can
occur.
THE INVENTION
It is an object of the present invention to provide equipment which
will generate a reset pulse for amicroprocessor not only when the
equipment is first turned on, but also if there are supply voltage
decreases which could lead to anomalies in the condition of the
microprocessor.
The apparatus is to have a wide range of application, that is both
the magnitude of supply voltage decrease which results in the
generation of a reset pulse and the duration of the pulse should be
adjustable. Additionally, the pulse which is generated when the
power is first applied should have a predetermined pulse width, so
that it can be differentiated from pulses resulting from a supply
voltage decrease.
In a preferred embodiment of the invention, the actual output from
the microprocessor is monitored so that a reset pulse is only
furnished when the operation of the microprocessor has been
affected. For example, a counter in the microprocessor may not have
reached a predetermined count within a predetermined time or a
voltage may not have reached a certain value within a given time.
Such malfunction would prevent the generation of pulses which
otherwise appear at regular intervals at an output of the
microprocessor. Failure to receive such pulses from the
microprocessor causes the generation of the reset pulse.
Preferably, a switch connected to the circuit of the present
invention receives the pulses from the microprocessor. Operation of
the switch prevents a capacitor in the circuit from reaching a
predetermined voltage, while lack of such pulses allows it to reach
the voltage. When the capacitor reaches the predetermined voltage,
the reset pulse is furnished.
The switch may be a transistor switch, either a standard transistor
or a field effect transistor being suitable. When any such
transistor switch is used, the apparatus of the present invention
can readily be constructed in integrated circuit form.
DRAWINGS ILLUSTRATING A PREFERRED EMBODIMENT
FIG. 1 is a first embodiment of a circuit according to the present
invention;
FIG. 2 is a second embodiment of the circuit of the present
invention;
FIG. 3 shows the variation with respect to time of the voltages in
different parts of the circuit of FIG. 2.
DESCRIPTION OF PREFERRED EMBODIMENTS
In FIG. 1, the supply voltage is applied between a line 1 and a
reference potential which may be ground potential. A capacitor 2 is
connected to line 1 and a resistor 3 is connected from the other
terminal of capacitor 2 to ground potential. A diode 4 is connected
in parallel with resistor 3 with the anode of diode 4 being
connected to ground potential. A protective resistor 5 is connected
between the common point of capacitor 2 and resistor 3 and the
inverting input of a difference amplifier 6. The direct input of
amplifier 6 is connected to a voltage divider consisting of
resistors 7 and 8. Resistor 7 is connected to line 1, while
resistor 8 is connected to ground potential. The output of
difference amplifier 6 is connected through to a resistor 9 to
supply line 1 and to its direct input through a resistor 10. The
reset pulse which is the subject of the present invention is
derived from the output of difference amplifier 6 and applied to a
microprocessor M at reset input terminal M-R.
OPERATION
After the supply voltage is first applied, the voltage at the
inverting input of difference amplifier 6 is higher than that at
its direct input. Therefore a "0" signal appears at the output of
difference amplifier 6. The signal may be used to reset the
microcomputer M. Capacitor 2 now starts to charge through resistor
3 so that, after a predetermined time, the output of difference
amplifier 6 switches to a "1" signal. If the value of resistors 7
and 8 are given, the time at which the circuit switches, and
therefore the duration of the "0" pulse, is determined in the main
by the time constant of the RC circuit consisting of resistor 3 and
capacitor 2.
If the supply voltage decreases by an amount which exceeds the
forward voltage drop across the diode, capacitor 2 starts to
discharge through diode 4. If, thereafter, the supply voltage is
raised, then, depending upon the threshold voltage which is
determined by resistors 7, 8 and 10, a pulse is generated whose
pulse width depends on the value of resistor 10. The magnitude of
voltage drops for which a pulse is generated thus can be defined
exactly by fixing the values of resistors 7, 8 and 10. If a
sensitive operational amplifier, such as, for example, type LM 139
of the firm National Semiconductor is utilized then voltage drops
of as little as 0.5 V can be detected since the threshold can be
fixed to be near zero.
Embodiment of FIG. 2: The power supply line is denoted by reference
numeral 11. A capacitor 12 is connected to supply line 11, the
other terminal of capacitor 12 being connected through a resistor
13 and the collector-emitter circuit of a transistor T having a
base 14 to ground potential. The inverting input of an operational
amplifier 15 is connected to the common point of capacitor 12 and
resistor 13. The direct input of operational amplifier 15 is
connected to the tap of the voltage divider constituted by resistor
16 and 17. Specifically, one terminal of resistor 16 is connected
to supply line 11 and one terminal of resistor 17 is connected to
ground potential. A resistor 18 is connected between the output of
operational amplifier 15 and supply line 11, while a resistor 19 is
connected between the output and the inverting input. A resistor 20
is connected from the output of operational amplifier 15 to its
direct input. The reset pulse is derived from the output of
operational amplifier 15.
An input terminal 21 is connected through a resistor 22 and a
capacitor 23 to the base 14 of transistor. Additionally, a diode 24
and a resistor 25 are connected between the base of transistor 14
and ground potential. The latter components constituted a
protective circuit for the transistor.
OPERATION
The operation of the circuit of FIG. 2 will be explained with
reference to FIG. 3. Operational amplifier 15 is connected as a
comparator whose thresholds are determined by resistors 16, 17 and
20. In particular, the hysteresis of the comparator is determined
by resistor 20 which thus determines pulse width of the output
pulse. Because of resistor 19 and capacitor 12, the circuit acts as
an RC oscillator whose frequency is determined by the value of
these two elements. If the polarity of the output symbol is to be
reversed, capacitor 12 may be connected to ground potential. The
specific connection depends on the desired potential at the output
of operational amplifier 15 after the supply voltage has been
switched in.
The variation with respect to time at the inverting input of
operational amplifier 15 is shown in FIG. 3a, while FIG. 3b
illustrates the variation with respect to time at the direct input.
FIG. 3c shows, in full line, the pulses P on line 21 and, in broken
line, the switch-over time of comparator 15. When the supply
voltage is first switched on, the potential at the inverting input
exceeds that at the direct input. The output of the operational
amplifier therefore is an "0" signal, which is used to reset the
apparatus connected to the output of the operational amplifier e.g.
microprocessor M' . Capacitor 12 starts to charge through resistor
19, so that comparator 15 switches after a predetermined time
interval (broken line, FIG. 3c . The signal at its output is now a
"1" signal which discharges the capacitor. If, after the
microprocessor M' has been reset, a program begins to run which,
after it is completed or, for a longer program, at predetermined
time intervals, causes a pulse P to be generated at the output on
line 21 of the microprocessor M' in accordance with a program which
has been pretested, then an omission of the pulse at line 21 is
indicative of a voltage drop. Thus if such a voltage drop occurs, a
pulse will not appear at input 21 to the transistor T in time to
prevent capacitor 12 from discharging to such an extent that the
upper threshold voltage which is shown as a dot-dash line in FIG.
3a is reached. The comparator switches so that the reset pulse
again appears at the output M-R. Because of positive feedback
resistor 20, the voltage at the direct input of operational
amplifier 15 also drops. Capacitor 12 discharges through resistor
19 until the lower threshold is reached. Thereafter, the output of
the comparator is again a "1" signal. The computer is again ready
for operation so that a new program can run.
The above circuits are easy to manufacture as integrated circuits.
It is particularly advantageous to incorporate them in the
microcomputer.
Many variations and changes of the above described circuits will be
readily apparent to one skilled in the art and are intended to be
encompassed by the following claims:
* * * * *